Conventionally lithographic printing plates are produced from radiation-sensitive plates comprising a radiation-sensitive composition coated on a suitable substrate. In use of the radiation-sensitive plate, the coating is image-wise exposed to radiation so that parts of the composition are struck by the radiation and parts are not. The radiation-struck and non-radiation-struck parts have differing solubilities in developer liquids and thus the more soluble parts can be selectively removed by application of such a liquid to leave an image on the substrate constituted by the less soluble parts.
For environmental and health reasons there has been an increasing tendency for wholly aqueous or substantially aqueous based solutions, rather than organic solvents, to be used as the developer liquids. For these solutions to be effective, the radiation-sensitive composition must be soluble, or at least swellable, in such solutions. In the case where the major component of the composition is a polymeric compound it follows that this compound must contain pendant groups such as carboxylic acid groups which render it soluble or swellable in aqueous neutral or alkaline solutions. However, such pendant groups, when present in sufficient quantity in the polymeric compound to provide adequate development when used in a radiation-sensitive composition, tend to cause the image to have high hydrophilicity and lower ink receptivity than is desirable. Reduction of the number of solubilising pendant groups, whilst improving the ink receptivity of the image, causes an unacceptable decrease in the developability of the radiation-sensitive composition in aqueous-based developing liquids.